An organic electroluminescence (EL) device is a promising solid-state emitting type inexpensive and large full-color display device, and has been extensively developed. In general, an organic EL device includes an emitting layer and a pair of opposing electrodes holding the emitting layer therebetween. When an electric field is applied between the both electrodes, electrons are injected from the cathode and holes are injected from the anode. The electrons recombine with the holes in the emitting layer to produce an excited state, and energy is emitted as light when the excited state returns to the ground state.
Conventional organic EL devices have a higher driving voltage than that of an inorganic light-emitting diode. The luminance or luminous efficiency thereof is also low, and their properties tend to deteriorate significantly. For these reasons, conventional organic EL devices have not been put in a practical use. Although recent organic EL devices have been improved gradually, further prolongation of lifetime, improvement in luminous efficiency or the like has been demanded.
The performance of an organic EL device has been gradually improved with improvements in emitting materials for an organic EL device. Improvement in luminous efficiency and prolongation of lifetime of an organic EL device is an important subject which leads to lowering in consumption power and improvement in durability of a display. Although luminous efficiency and lifetime of an organic EL device have been improved as a result of various studies, further improvement is demanded.
In order to solve these problems, Patent Documents 1 to 6 each disclose an organic EL device in which an anthracene derivative having dibenzofuran as a substituent is used as an emitting material. Although luminous efficiency is improved by using these materials, but the improvement was not sufficient. Further improvement in luminous efficiency and prolongation of lifetime has been required.
On the other hand, Patent Documents 4, 7 and 8 each disclose an emitting material having a fused dibenzofuran structure. However, an organic EL device using this emitting material has a defect that it has a poor efficiency and a significantly short life.